1. Field of the Invention
This invention relates to a method for producing a multilayer circuit board and, more particularly, to a method for producing a multilayer circuit board with an interposer used for a chip-size package.
2. Description of the Prior Art
In recent years, as the demand for the circuit board to have increasingly higher density and finer pitch increases, three-dimensionally wired multilayer circuit boards have been increasingly used. The multilayer circuit board has semiconductor devices mounted thereon. The multiplayer circuit board usually has terminals larger in pitch than the terminals of the semiconductor devices. Due to this, as shown in FIG. 13, an interposer 3, which has on one side thereof terminals 5 formed with pitches corresponding to the terminals 4 of the semiconductor device 1 and has on the other side thereof terminals 7 formed with pitches corresponding to the terminals 6 of the multilayer circuit board 2, is interposed between the semiconductor device 1 and the multilayer circuit board 2, so that the terminals 4 of the semiconductor device 1 and the terminals 6 of the multilayer circuit board 2 are electrically connected through the interposer 3.
It is known that such a multilayer circuit board 2 with the interposer 3 is produced, for example, by the method that insulating layers 2a and conductive layers 2b formed in the form of a predetermined circuit pattern are laminated alternately and also the conductive layers 2b are allowed to conduct through inner via holes 2c to thereby produce the multilayer circuit board 2 in the known manner, and then insulating layers 3a and conductive layers 3b formed in the form of a predetermined circuit pattern are laminated alternately on the multilayer circuit board 2 thus produced and also the conductive layers 3b are allowed to conduct through inner via holes 3c to thereby produce the interposer 3 in the known manner.
However, with this producing method of the multilayer circuit board 2 with the interposer 3, if the production of the interposer 3 fails after the production of the multilayer circuit board 2, not only the interposer 3 but also the multilayer circuit board 2 must be scrapped, thus suffering a considerable loss in the manufacturing process.
It may be conceivable that the multilayer circuit board 2 and the interposer 3 are produced separately, first, and then are joined together, but since the interposer 3 is so thin and limp that it is hard for the both to be aligned with and joined to each other with accuracy.
It is the object of the invention to provide a producing method of a multilayer circuit board for ensuring that a circuit board, such as an interposer, is provided on the multilayer circuit board.
The present invention is directed to a novel method for producing a multilayer circuit board comprising the step of forming a circuit board on a support board; the step of forming a multilayer circuit board separately from the circuit board; the step of joining the circuit board formed on the support board to the multilayer circuit board; and the step of removing the support board.
According to this producing method, the circuit board and the multilayer circuit board can be allowed to be produced separately. Hence, even if the production of the circuit board fails after the production of the multilayer circuit board, it is possible to scrap the circuit board only and there is no need to scrap it together with the multilayer circuit board, differently from the conventional method. Thus, losses in the manufacturing process can be reduced, thus achieving saving of material resources and reduction of manufacturing costs.
Besides, although the circuit board is so thin and limp, since it is formed on the support board, the reliable and easy joining can be effected. Hence, according to this method, the circuit board can surely be jointed to the multilayer circuit board.
In addition, according to this producing method, since the support board serves to prevent contraction of the resin of the insulating layers in the manufacturing process of the circuit board, the displacement between the layers can well be prevented. Hence, the circuit board can be produced with fine pitches with accuracy, as compared with the conventional method that after the multilayer circuit board is produced, the circuit board is produced directly on it.
Further, according to this producing method, since the support board enables the surface of the insulating layer, which was in contact with the support board of the circuit board, to smoothly be formed, improved reliability for connection with an external circuit board can be provided.
According to the present invention, it is preferable that the circuit board formed on the support board has a multitiered structure. Preferably, the circuit board formed on the support board is an interposer for electrically connecting between a semiconductor device and the multilayer circuit board.